A/C system is intermittent

[TGMarrs]

I am usually pretty quick to troubleshoot and fix everything on my coach, but this one has me stumped.

2003 Monaco Executive 44' with three DuoTherm A/C units with the 5 button comfort control units (x2).

For 80% of the time, air conditioning works great. Sometimes the A/C just stops working for awhile. I keep the system on auto fan, and each unit cycles on and off fine for a day or two, then we will notice the coach is getting warmer and the units are no longer coming on. There is nothing you can do to get A/C again until a few hours later when it just decides to work again. It will then operate normal for another 24-48 hours.

Both the front and rear units are on completely separate circuits, controlled by separate thermostats and I don't know of any connection between the two systems, but when the problem comes they both stop cooling.

When the cooling stops, the fans will work fine if I take them off auto, and sometimes when I turn a fan on low or high the compressor will come back on and start cooling us off... Sometimes.

I have thought perhaps both compressors froze up at the same time, but one time I also tried the middle unit that was not being used and the compressor would not come on that one either until the problem self corrected, so that's not it. Any ideas?

[RV Wizard]

As you probably already know, an intermittent issue is the hardest to troubleshoot. You can guess that something might be a problem and do whatever changes to correct and then just wait and see if it has indeed fixed the problem or you will have to wait until the unit fails and start the troubleshooting process. As long as the unit(s) do function all test will show everything is good. I would ask if the coach has an EMS? If so what power source were you using when the malfunction occurred? I feel like the issue is probably a DC voltage control circuit but would check 120 VAC wiring connections at the distribution panel and transfer switch just to eliminate that possibility. What kind of test equipment do you have? If you can get your hands on a Power Probe, it would be very beneficial in troubleshooting DC circuits. Maybe you could borrow or rent one when the problem re-occurs.

[TGMarrs]

I was thinking power issues, as we first noticed the issue on 30amp and the EMS was managing loads, however turning everything off except the front A/C didn't help. The next time it happened we were plugged into 50 amp service. I have yet to see it happen on generator, but we have never run the genny long enough to know.

Testing equip - I have a good voltmeter. Not sure what the other instrument you mentioned is.

Is there any connection you know of between the front and rear system? That is the part that has me puzzled... Why both would do the same thing at the same time with no apparent connection or sharing of any component between them...

[jettyjock]

A lot of units have a low and a high pressure switch that will shut off the compressor. Both switches will cause the unit to cycle on and off. The only way to trouble shoot it is to put gauges on it while its running.

[RV Wizard]

While the front and rear units are not controlled by the same thermostat and therefore, independent of each other; they do share a 12 VDC and 120 VAC power source. 12 VDC is for controlling the units, although the EMS may interrupt this circuit when shedding loads. You should be able to verify if 12 VDC is present when the unit fails. Make sure the unit is not just in a time delay situation first. If you do not have 12 VDC at the roof unit then check the EMS and distribution panel to find out where you are loosing it. If you do have 12 VDC verify 120 VAC feeding the unit. A power probe is a glorified 12 VDC test light that allows you to also check for ground as well as apply 12 volt + and - to the probe.

[TGMarrs]

OK, took awhile for it to happen again... Was working great plugged into 30 amp campsite for 2 weeks. We drove away and tried to use AC on the generator.... No luck.

While it was not working, I had 13v DC at the thermostats, and 110v AC good on the roof units. And as stated before, the fans still work fine during these periods, just the compressor will not kick on. Still stumped!

[RV Wizard]

Quote:

Originally Posted by TGMarrs OK, took awhile for it to happen again... Was working great plugged into 30 amp campsite for 2 weeks. We drove away and tried to use AC on the generator.... No luck. While it was not working, I had 13v DC at the thermostats, and 110v AC good on the roof units. And as stated before, the fans still work fine during these periods, just the compressor will not kick on. Still stumped!

What was the voltage under load at the campsite? I take it that you had 110 vac to the roof units under load. Did you ever see it dip below the 110 vac level? Did you ever hear the compressors try to start up? Where was the fan stetting at when you state they would run? Did you ever notice the fans briefly stopping? I would verify that all air conditioning conductors connections be checked to be clean and tight. Also check the conductor connections of the generator at all point tot he distribution panel (that includes the transfer switch). Let us know what you find.